platform/x86: thinkpad_acpi: Fix inconsistent indenting

Eliminate the follow smatch warning:

drivers/platform/x86/thinkpad_acpi.c:7942 volume_write() warn:
inconsistent indenting.
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Link: https://lore.kernel.org/r/1621837438-70790-1-git-send-email-jiapeng.chong@linux.alibaba.comSigned-off-by: Hans de Goede <hdegoede@redhat.com>